1. Field of the Invention
The present invention relates to a valve employing a quick exhaust feature that has an audible sound or "honking" generated during a quick exhaust function. More particularly, the invention relates to an anti-lock braking system ("ABS") modulator valve that regulates air flow to and from a wheel brake in a heavy vehicle and encounters an audible sound during release of the service brakes.
2. Discussion of the Art
A quick exhaust feature, using a diaphragm that is normally biased to a closed position with its valve seat via a biasing spring, has proved useful in quickly and effectively exhausting a large amount of air from a brake chamber during release of the service brakes. Specifically, a major portion of return service air from the brake chambers is expelled through an exhaust port of the modulator valve during brake release. The return service air has a slightly higher pressure and thus exerts a slightly greater force on the exhaust diaphragm than the combined forces resulting from a pilot pressure and spring loading on an opposed or rear face of the exhaust diaphragm. The diaphragm is lifted from its seat, the service air is expelled through the exhaust port, and then the diaphragm is re-seated. That is, as the service air is expelled through the exhaust port, the pressure drops slightly below the combined forces exerted by the pilot pressure and the spring load on the opposite face of the exhaust diaphragm. The exhaust diaphragm thus reseats and blocks the service air from expelling through the exhaust port. However, an unbalanced pressure situation occurs again across the exhaust diaphragm causing it to lift from the valve seat and expel the service air through the exhaust port. This oscillating motion of the exhaust diaphragm occurs within a very short time frame and results in an audible honking sound during brake release.
Although there is no problem associated with the sound, it is disturbing because of the high-pitched noise. A vehicle operator could become concerned that the brakes are not functioning properly when, in fact, the valve is operating properly and the service brakes are being released in an effective manner not possible with prior art arrangements.
Accordingly, a need exists to maintain the quick exhaust of air from the brake chambers/modulator valve so that all of the attendant features and benefits of that valve are maintained in conjunction with a decreased or muffled noise associated with the release of the service brakes.